1. Field of the Invention
The present invention relates to a circulating type ball spline bearing comprising a cylindrical outer sleeve having, on its internal surface, a plurality of axially extending raceway grooves, a spline shaft adapted to be movably received within said cylindrical outer sleeve and having, on its outer periphery, a plurality of axially extending raceway grooves in facing relation with said respective axially extending raceway grooves of the cylindrical outer sleeve, and a plurality of balls intervening between the facing pairs of the axially extending raceway grooves of said cylindrical outer sleeve and spline shaft, respectively, wherein by endlessly circulating said balls through said cylindrical outer sleeve, a rectilinear relative motion may be realized between said cylindrical outer sleeve and spline shaft with a torque being transferred therebetween.
2. Description of the Prior Art
Heretofore, various kinds of inventions have been made regarding circulating type ball spline bearings but they had not a few disadvantages regarding the size and rigidity so that a ball spline bearing having a small size yet a high rigidity was demanded in the art.
For example, U.S. Pat. No. 3,659,435 specification, published on May 2, 1977 disclosed a circulating type ball spline shaft having a cylindrical outer member or outer sleeve wherein each of the ball return bores is formed therewithin on the plane including the centers of two adjacent load carrying balls as seen in the cross section in the cylindrical outer member, so that the wall thickness of the cylindrical outer member was unavoidably become greater, thus resulting in a restriction of miniaturization thereof.
On the other hand, U.S. Pat. No. 4,375,305 specification, published on Mar. 1, 1983 essentially employed a ball retainer in a cylindrical outer member, while U-shaped channels are radially cut into the inner periphery of said cylindrical outer member to form non-load carrying ball grooves and load carrying ball grooves, respectively, in said cylindrical outer member, and these grooves may be formed respectively or simultaneously by a broaching or slotting operation, thereby enhancing the efficiency of the grooving operation to a considerable degree.
Moreover, according to the above-mentioned invention, each of ball turning grooves is arcuately bent toward the spline shaft side so that the size of the bearing can be much reduced than that of the prior art spline bearing but to avoid any accidental falling-off of the non-load carrying and load carrying balls from the U-shaped grooves, they must be retained in the cylindrical outer member with the aid of a retainer, thereby not only inevitably requiring much greater number of constructional parts for assembling the bearing but also giving rise to cumulative error in the assembling precision that will cause incidental falling-off of the balls from the race way grooves and further increasing sliding friction due to undesirable contact in operation between the retainer and the circulating balls.